What happened to this stealth fighter remains a mystery

(U.S. Air Force photo by Senior Airman Alexander Cook)

More pieces from an F-35 stealth fighter that disappeared in the Pacific have been found, the Japanese defense minister revealed May 7, 2019.

A Japan Air Self-Defense Force F-35A Lightning II Joint Strike Fighter piloted by Maj. Akinori Hosomi mysteriously vanished from radar on April 9, 2019. The day after the crash, pieces of the tail were found floating on the surface of the water, but the rest of the fifth-generation fighter was nowhere to be found.

The fighter, believed to be lying somewhere on the ocean floor, has been missing for weeks, despite the best efforts of the US and Japanese militaries to find it.

Japanese Defense Minister Takeshi Iwaya announced May 7, 2019, that parts of the flight recorder and cockpit canopy had been discovered at an unspecified location on the ocean floor, CNN reported. The flight recorder was retrieved by a US Navy salvage team dispatched to assist in the search.

First operational F-35A Lightning II presented to JASDF's 3rd Air Wing at Misawa Air Base.

(U.S. Air Force photo by Tech. Sgt. Benjamin W. Stratton)

The defense minister said the flight recorder is in "terrible" condition. Critical memory components are reportedly missing, meaning that key data about the crash, the first for an F-35A, may be unavailable. Exactly what happened to the stealth fighter remains a mystery.

The downed F-35, which was built by Lockheed Martin but assembled by Mitsubishi Heavy Industries. Ltd., is one of a growing fleet of Japanese stealth fighters. In response to the crash, Japan grounded its remaining F-35s. They will remain on the ground while the related investigation is ongoing.

Japan currently has 12 F-35s, but it has another 147 stealth fighters on order. B variants with that need little runway to take off and land are expected to eventually serve on Japanese light aircraft carriers while the A variant will become the primary fighter of the Japanese air force.

The search for the missing fighter and its pilot is expected to continue.

This article originally appeared on Business Insider. Follow @BusinessInsider on Twitter.